Process of manufacturing photographic silver halid emulsions



April 24, 1928. 1,667,589

w. DIETERLE ET AL PROCESS OF MANUFACTURING PHOTOGRAPHIC SILVER HALIDEMULSIONS Filed July 12, 192

Inventor Patented Apr. 24, 1928.

UNITED STATES PATENT OFFICE.

WALTER mn'rnam AND or'ro m'r'rnms, or DESSAU, AND rosary mirrsror'rnn,or

IBERLIN-FRIEDENAU, GERMANY, assxenoas m I. a. ramannmnus'ram nx'rmn-GEsELLsonAr'r, or FRANKFORT-ON-THE-MAIN, GERMANY.

PROCESS OF MANUFACTURING PHOTOGBAPHIC SILVEfi HALID EMULSION.

Application filed J'u1y 12, 1926, Serial No. 122,038, and in GermanyOctober 7, 1925.

In manufacturing photographic silver .halid emulsions the qualities ofthe colloidal substance have a great influence on the photographicproperties of the emulsion. The

6 sensitivity of the emulsion, e. g., depends in a high degree on thecolloid employed. While it is easy to obtain with a certain type ofgelatine a high sensitivity, other types of gelatine yield emulsions ofpractical y sufli- 10 cient sensitivity with great difliculity or not atall. It is possible, indeed, to increase the sensitivity to a certainextent by moderately heating it for some time, but this so-calledripening process must not be pushed further 1 than to a limit which maynot be transgressed if the tendency of forming fog isto be avoided.Ripening-time and ripeningtemperature depend upon the sort of thecolloid em loyed.

It has been found that high-speed silver halid emulsions free from fogmay be made.

by adding, in emulsion making, substances which may be produced byelectro-dialysis from pure or impure proteins, e. g., from gelatine orglue. These substances may be added to the raw materials of theemulsion,

during emulsion making or to the finished emulsion.

The substances employable for this pur- 80 pose are prepared in knownmanner by electro-dialysis of aqueous solutions of proteins betweendiaphragms of definite potential. When aqueous solutions of gelatine oranother protein are dialyzed between two diaphragms, various physicaland chemical reactions take place at the same time. Prod-- nets of ionicdispersity migrate to the electrodes and here they are discharged andprecipitated. Hereby a diminution of the elec- 40 trolyte is effectedwhich causes the precipitation of certain proteins insoluble in purewater. Thus globulines, e. g., are precipitated in the intermediatespace by the electro-dialysis of glue. In addition a more or less largeelectrophoresis takes place. Moreover colloidall dispersed"protein-particles of unknown c emical constitution migrate through thediaphragms to the electrodes or to-the spaces extending in front ofthem. 60 The anode-substances are separated and be inspissated andsolidify to a light yellow mass of conchoidal fracture, smelling in- Itensely of soap when wet;

The substances separated at the electrodes have the property ofincreasing the sensitivity of silver halid emulsions. According to theapplication in view or the type of emulsion to be manufactured from theelatine, there may be employed the pro ucts obtained at the anode, orthose obtained at the cathode or mixtures of both.

The improvement in sensitivity effected by this process is evident fromthe following comparison:' I

A gelatine for emulsions is worked up in known manner to a photographicemulsion which is eflicaciously ripened by; heating it at C. during 60minutes. The characteristic curve indicated in the drawing'by (1corresponds to this emulsion. This curve represents the relation betweenthe densities of the developed emulsion and the logarithms of exposure.The shape of the curve a shows that the emulsion has no greatsensitivitgbeginning only at a rather high value of t abscissa, namely, 6. Whenripening is pushed further the emulsion begins to fog.

\Vhen to'the same gelatine is added 1% of the dried product of theelectro-dialysis of gelatine obtained at the cathode, and it is thenworked up in the same manner, a photographic emulsion is produced thecharacteristic curve of which is indicated in the drawing by Fb. Itheginsat the abscissavalue.of 3 with an ordinate-value of 2 and endswith the ordinate value 265, i. e., this emulsion-has no greater fogthan the first, but it has much increased insensitivity and in coveringpower.

The extracts from proteins produced by electro-dialysis are generallynot neutral, but acid or alkaline. But in some emulsion making processesit is not advisable to change the concentration of hydrogen-ions byadding other substances. It is often useful therefore, to neutralize theelectro-dialytically separated extracts by means of alkaline or acidagents and to dry them, if it 6 is necessary, by evaporating.

We claim:

1. A process of making photographic s'ilver halid emulsions whichcomprises adding during emulsion making substances extract- 10 able fromproteins by electro-dialysis.

2. Silver halid emulsions containing added i thereto substancesextractable from proteins by electro-dialysis.

3. Photographic layers comprising silver halid emulsions containingadded thereto substances extractable from proteins by electro-dialysis.

In testimony whereof we aifixour signatures.

WALTER DIETERLE. OTTO MATTHIES.

JOSEF REITSToTTER.

